Democratic Sen. Barbara Boxer wrote the agency showing water supplies at thousands of schools have been found to contain unsafe levels of lead, pesticides and dozens of other toxics.
Contaminants have surfaced at public and private schools in all 50 states, and in small towns and inner cities alike over the last decade. But the AP found the problem has gone largely unmonitored by the federal government, even as the number of water safety violations has multiplied.
Boxer, who chairs the Senate committee that oversees the EPA, said she took action out of "deep concern" that polluted water supplies could be harming school children as their young bodies are developing.
"The EPA is responsible for overseeing the safety of our nation's drinking water systems," Boxer wrote in a letter sent Monday to EPA Administrator Lisa Jackson. "I am sure that you recognize the importance of acting quickly to address any report of pollution in the water our children drink."
An EPA spokeswoman had no immediate comment.
The AP's analysis focused on schools with wells, the 8 to 11 percent of the nation's schools for which the EPA collects drinking water quality data.
In the past, EPA officials have said that schools with unsafe water represent only a small percentage of the nation's 132,500 public and private schools. They also have said the agency lacks the authority to require that all schools test their water, and can only provide guidance on environmental practices.
EPA officials also acknowledge the agency's database of schools in violation of the Safe Drinking Water Act is plagued with errors and omissions. The problem goes beyond schools that use wells, since schools in Baltimore, Seattle and other large cities that draw water from public utilities have shown contamination, as well.
Citing a "lack of a national strategy for monitoring schools' water," Boxer asked EPA officials to explain how the agency oversees and enforces drinking water quality rules to her committee staff.
Boxer also requested an outline of specific actions taken to address problems in schools' drinking water, a timetable for when those efforts will be completed and a report of any new legal authorities needed to protect students from toxic drinking water.